SPOILER ALERT: This blog is published ahead of the screening of Prometheus on Sky Showcase on Sunday at 8pm. Do not read if you have not seen the film and don't want to know anything about it.

"A king has his reign, and then he dies. It's inevitable" - Meredith Vickers

It is the year 2093. Mankind's plan to visit everything that cavemen point at in pictures has finally reached fruition, in tandem with Weyland Corp's top secret Operation Pretend to Be Dead But Really Just Hide on a Spaceship Even Though It Makes No Sense. Finally, we are about to answer humanity's most important questions. Who are we? Why are we here? Wouldn't it be cleverer to run away from that falling spaceship sideways? All the biggies.

But there are snags. The crew may have inadvertently stumbled upon an intergalactic weapon silo. The weapons might be about to destroy Earth. The creatures who made them probably invented humans in the first place. More pressingly, none of the ship's biologists can tell the difference between "harmless animal" and "obviously dangerous alien death-snake", everyone displays a dangerously cavalier attitude to breathing in unknown atmospheres, and our heroine's mutant buzzkill of a boyfriend has just knocked her up with a giant thrashing squid.

This is Prometheus. It's the story of Ridley Scott's attempt to save the Alien franchise from campy sequels and redundant spinoffs and gifs that do nothing but make you sad. More specifically, it's the story of how he bodged the job and ended up with a mess of a film that has all the ambition in the world, but zero inclination to see any of it through.

"Mortal after all" – David

Prometheus is best when it ditches the existential mumbo-jumbo and focuses on the body-horror thrills that made Alien so much fun. And no sequence does this better than the scene where Noomi Rapace jumps into a medical pod to have an impromptu caesarean. Very clearly intended to be the equivalent of Alien's chestburster sequence, we see the lot – a bulging stomach, graphic surgery and then the closeup terror of Rapace as she's confronted with the awful sight of her wriggling, writhing alien baby.

And yet, even this bit isn't flawless. I realise that it's set a few decades into the future, but there's no way that anaesthetic has got that good. When I was younger, I had a small cyst removed from behind my ear. It was agony, and it was agony for days afterwards. But Rapace is up on her feet seconds later, a bunch of industrial-looking staples jammed through her gut, gambolling around the spaceship like a lamb in springtime.

Prometheus is riddled with inconsistencies like this. In another scene, they find a giant alien head, and the first thing they do is electrocute it until it explodes. That's not what scientists do. It's what eight-year-old boys do the first time they're left alone with an egg and a microwave.

"There is only death here now" – Elizabeth Shaw

Oh God, nothing is as frustrating as this film's climax. When I saw Prometheus at the cinema – at the Imax on opening night, full of people desperate to love it – there were snorts of derision when Charlize Theron revealed that Peter Weyland was (dun dun duuun) her father all along. And it just gets sillier from there. The Engineers just so happen to be about to blow up Earth. Rapace's alien squid suddenly becomes enormous in defiance of the law of conservation of mass. Charlize Theron fails to run sideways like a normal person would. And then, perhaps most annoyingly of all, nothing really gets solved. The whole thing is just a setup for Prometheus 2: Let's Hunt For Alien Jesus With a Decapitated Robot Head. And there aren't even any poxy Xenomorphs in it. What a swizz.

Talking points

• If you're looking for an exhaustive list of everything that's wrong with Prometheus from a logical perspective, We Got This Covered has got it covered.

• One thing I would watch Prometheus 2 for: an explanation about why Guy Pearce was in the film at all. You could have chopped him out of Prometheus completely and nobody would have noticed – surely he's part of larger story, isn't he? Surely.

• Does Prometheus make you more or less excited about Ridley Scott's proposed Blade Runner sequel? It's less excited, isn't it? It's OK, you can tell me.